Provided it's just rust that is the issue, give electrolysis a shot. If it's not only rust in it that you're worried about, give it a 15-24 hour vinegar bath, wash it off good, then try electrolysis.
Here is a short-ish video on how to make an electrolysis setup.
[ame]https://www.youtube.com/watch?v=sOYLQ86IdUk[/ame]
Not the best video out there, but a fairly short one (10 minutes) that decently explains the process. I use electrolysis for removing rust from parts all the time, by far the best method I have found for it.
Granted his example wasn't that rusty to begin with, this is an excellent method. There are a ton of videos out there if you look for them that will probably explain the process a little better, but will definitely be longer.
Edit:
If anyone can tell me how to remove the video from this post and only post the link, that would be great.